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Chin. Phys. B  
  Chin. Phys. B--2010, Vol.19, No.5
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A method for extracting human gait series from accelerometer signals based on the ensemble empirical mode decomposition

Fu Mao-Jing, Zhuang Jian-Jun, HouFeng-Zhen, Zhan Qing-Bo, Shao Yi, Ning Xin-Bao
Chin. Phys. B, 2010, 19 (5): 058701 doi: 10.1088/1674-1056/19/5/058701
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In this paper, the ensemble empirical mode decomposition ({EEMD}) is applied to analyse accelerometer signals collected during human normal walking. First, the self-adaptive feature of {EEMD} is utilised to decompose the accelerometer signals, thus sifting out several intrinsic mode functions {(IMFs}) at disparate scales. Then, gait series can be extracted through peak detection from the eigen {\rm IMF} that best represents gait rhythmicity. Compared with the method based on the empirical mode decomposition ({EMD}), the {EEMD}-based method has following advantages: it remarkably improves the detection rate of peak values hidden in the original accelerometer signal, even when the signal is severely contaminated by the intermittent noises; this method effectively prevents the phenomenon of mode mixing found in the process of {EMD}. And a reasonable selection of parameters for the stop-filtering criteria can improve the calculation speed of the {EEMD}-based method. Meanwhile, the endpoint effect can be suppressed by using the {auto regressive and moving average} model to extend a short-time series in dual directions. The results suggest that {EEMD} is a powerful tool for extraction of gait rhythmicity and it also provides valuable clues for extracting eigen rhythm of other physiological signals.

Periodic-cylinder vesicle with minimal energy

Zhou Xiao-Hua
Chin. Phys. B, 2010, 19 (5): 058702 doi: 10.1088/1674-1056/19/5/058702
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We give some details about the periodic cylindrical solution found by Zhang and Ou-Yang in [1996 {\em Phys. Rev.} E {\bf 53} 4206] for the general shape equation of vesicle. Three different kinds of periodic cylindrical surfaces and a special closed cylindrical surface are obtained. Using the elliptic functions contained in \emph{mathematic}, we find that this periodic shape has the minimal total energy for one period when the period--amplitude ratio $\beta\simeq1.477$, and point out that it is a discontinuous deformation between plane and this periodic shape. Our results also are suitable for DNA and multi-walled carbon nanotubes (MWNTs).
GENERAL

Approximate symmetry reduction for perturbed nonlinear Schr?dinger equation

Xie Shui-Ying, Lin Ji
Chin. Phys. B, 2010, 19 (5): 050201 doi: 10.1088/1674-1056/19/5/050201
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We investigate the one-dimensional nonlinear Schr\"{o}dinger equation with a perturbation of polynomial type. The approximate symmetries and approximate symmetry reduction equations are obtained with the approximate symmetry perturbation theory.

A new (2+1)-dimensional supersymmetric Boussinesq equation and its Lie symmetry study

Wang You-Fa, Lou Sen-Yue, Qian Xian-Min
Chin. Phys. B, 2010, 19 (5): 050202 doi: 10.1088/1674-1056/19/5/050202
Full Text: [PDF 101 KB] (Downloads:542)
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According to the conjecture based on some known facts of integrable models, a new (2+1)-dimensional supersymmetric integrable bilinear system is proposed. The model is not only the extension of the known (2+1)-dimensional negative Kadomtsev--Petviashvili equation but also the extension of the known (1+1)-dimensional supersymmetric Boussinesq equation. The infinite dimensional Kac--Moody--Virasoro symmetries and the related symmetry reductions of the model are obtained. Furthermore, the traveling wave solutions including soliton solutions are explicitly presented.

Asymptopic solution for a class of semilinear singularly perturbed fractional differential equation

Shi Lan-Fang, Mo Jia-Qi
Chin. Phys. B, 2010, 19 (5): 050203 doi: 10.1088/1674-1056/19/5/050203
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This paper considers a class of boundary value problems for the semilinear singularly perturbed fractional differential equation. Under the suitable conditions, firstly, the outer solution of the original problem is obtained; secondly, using the stretched variable and the composing expansion method the boundary layer is constructed; finally, using the theory of differential inequalities the asymptotic behaviour of solution for the problem is studied and the uniformly valid asymptotic estimation is discussed.

Some discussions about the variable separating method for solving nonlinear models

Ruan Hang-Yu
Chin. Phys. B, 2010, 19 (5): 050204 doi: 10.1088/1674-1056/19/5/050204
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Through analysing the exact solution of some nonlinear models, the role of the variable separating method in solving nonlinear equations is discussed. We find that rich solution structures of some special fields of these equations come from the nonzero seed solution. However, these nonzero seed solutions is likely to result in the divergent phenomena for the other field component of the same equation. The convergence and the signification of all field components should be discussed when someone solves the nonlinear equation using the variable separating method.

Adaptive co-evolution of strategies and network leading to optimal cooperation level in spatial prisoner's dilemma game

Chen Han-Shuang, Hou Zhong-Huai, Zhang Ji-Qian, Xin Hou-Wen
Chin. Phys. B, 2010, 19 (5): 050205 doi: 10.1088/1674-1056/19/5/050205
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We study evolutionary prisoner's dilemma game on adaptive networks where a population of players co-evolves with their interaction networks. During the co-evolution process, interacted players with opposite strategies either rewire the link between them with probability $p$ or update their strategies with probability $1-p$ depending on their payoffs. Numerical simulation shows that the final network is either split into some disconnected communities whose players share the same strategy within each community or forms a single connected network in which all nodes are in the same strategy. Interestingly, the density of cooperators in the final state can be maximised in an intermediate range of $p$ via the competition between time scale of the network dynamics and that of the node dynamics. Finally, the mean-field analysis helps to understand the results of numerical simulation. Our results may provide some insight into understanding the emergence of cooperation in the real situation where the individuals' behaviour and their relationship adaptively co-evolve.

Form invariance and new conserved quantity of generalised Birkhoffian system

Mei Feng-Xiang, Wu Hui-Bin
Chin. Phys. B, 2010, 19 (5): 050301 doi: 10.1088/1674-1056/19/5/050301
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A form invariance and a conserved quantity of the generalised Birkhoffian system are studied. Firstly, a definition and a criterion of the form invariance are given. Secondly, through the form invariance, a new conserved quantity can be deduced. Finally, an example is given to illustrate the application of the result.

Entanglement evolution in an anisotropic two-qubit Heisenberg XYZ model with Dzyaloshinskii-Moriya interaction

Chen Tao, Huang Yan-Xia, Shan Chuan-Jia, Li Jin-Xing, Liu Ji-Bing, Liu Tang-Kun
Chin. Phys. B, 2010, 19 (5): 050302 doi: 10.1088/1674-1056/19/5/050302
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This paper investigates the entanglement evolution of a two-qubit anisotropic Heisenberg XYZ chain in the presence of Dzyaloshinskii--Moriya interaction. The time evolution of the concurrence is studied for the initial pure entangled states $\cos \theta \left\vert 00\right\rangle +\sin \theta \left\vert 11\right\rangle $ and $\cos \phi \left\vert 01\right\rangle +\sin \phi \left\vert 10\right\rangle $ at zero temperature. The influences of Dzyaloshinskii--Moriya interaction $D$, anisotropic parameter $\varDelta$ and environment coupling strength $\gamma$ on entanglement evolution are analysed in detail. It is found that the effect of noisy environment obviously suppresses the entanglement evolution, and the Dzyaloshinskii--Moriya interaction $D$ acts on the time evolution of entanglement only when the initial state is $\cos \phi \left\vert 01\right\rangle +\sin \phi \left\vert 10\right\rangle $. Finally, a formula of steady state concurrence is obtained, and it is shown that the stable concurrence, which is independent of different initial states and Dzyaloshinskii--Moriya interaction $D$, depends on the anisotropic parameter $\varDelta$ and the environment coupling strength $\gamma$.

Unifying the theory of integration within normal-, Weyl- and antinormal-ordering of operators and the s-ordered operator expansion formula of density operators Hot!

Fan Hong-Yi
Chin. Phys. B, 2010, 19 (5): 050303 doi: 10.1088/1674-1056/19/5/050303
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By introducing the $s$-parameterized generalized Wigner operator into phase-space quantum mechanics we invent the technique of integration within $s$-ordered product of operators (which considers normally ordered, antinormally ordered and Weyl ordered product of operators as its special cases). The $s$-ordered operator expansion (denoted by $\circledS \cdots \circledS)$ formula of density operators is derived, which is $$\rho=\frac{2}{1-s}\int \frac{\d^2\beta}{\pi}\left \langle -\beta \right \vert \rho \left \vert \beta \right \rangle \circledS \exp \Big\{ \frac{2}{s-1}\left( s|\beta|^{2}-\beta^{\ast}a+\beta a^{\dagger}-a^{\dagger}a\right) \Big\} \circledS.$$ The $s$-parameterized quantization scheme is thus completely established.

Quantum phase transition and entanglement in Heisenberg XX spin chain with impurity

Chen Shi-Rong, Xia Yun-Jie, Man Zhong-Xiao
Chin. Phys. B, 2010, 19 (5): 050304 doi: 10.1088/1674-1056/19/5/050304
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In this paper, we study the quantum phase transition and the effect of impurity on the thermal entanglement between any two lattices in three-qubit Heisenberg XX chain in a uniform magnetic field. We show that the quantum phase transition always appears when impurity parameter is an arbitrary constant and unequal to zero, the external magnetic field and impurity parameters have a great effect on it. Also, there exists a relation between the quantum phase transition and the entanglement. By modulating the temperature, magnetic field and the impurity parameters, the entanglement between any two lattices can exhibit platform-like behaviour, which can be used to realize entanglement switch.

Unconditional preparation of multipartite continuous-variable entangled states among remote parties

Hu Xue-Yuan, Gu Ying, Gong Qi-Huang, Guo Guang-Can
Chin. Phys. B, 2010, 19 (5): 050305 doi: 10.1088/1674-1056/19/5/050305
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We demonstrate that the $n$-partite continuous-variable entanglement can be unconditionally prepared among $n$ parties that share no common past, from $n$ two-mode squeezed states. Both GHZ-like and cluster-like states can be generated for any nonzero squeezing in the entangled sources. An application of the resulting multipartite entangled state to a teleportation network is illustrated.

Three-party quantum secret sharing of secure direct communication based on χ-type entangled states

Yang Yu-Guang, Cao Wei-Feng, Wen Qiao-Yan
Chin. Phys. B, 2010, 19 (5): 050306 doi: 10.1088/1674-1056/19/5/050306
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Based on $\chi $-type entangled states and the two-step protocol [Deng F G, Long G L and Liu X S 2003 {\it Phys. Rev.} A {\bf68} 042317], a quantum secret sharing protocol of secure direct communication based on $\chi$-type entangled states $\vert \chi ^{00}\rangle _{3214} $ is proposed. Using some interesting entanglement properties of this state, the agent entirety can directly obtain the secret message from the message sender only if they collaborate together. The security of the scheme is also discussed.

Unified treatment for accurate and fast evaluation of the Fermi-Dirac functions Hot!

I. I. Guseinov, B. A. Mamedov
Chin. Phys. B, 2010, 19 (5): 050501 doi: 10.1088/1674-1056/19/5/050501
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A new analytical approach to the computation of the Fermi-Dirac (FD) functions is presented, which was suggested by previous experience with various algorithms. Using the binomial expansion theorem, these functions are expressed through the binomial coefficients and familiar incomplete Gamma functions. This simplification and the use of the memory of the computer for calculation of binomial coefficients may extend the limits to large arguments for users and result in speedier calculation, should such limits be required in practice. Some numerical results are presented for significant mapping examples and they are briefly discussed.

Thermodynamic properties of a finite Bose gas in a harmonic trap

Wang Jian-Hui, Ma Yong-Li
Chin. Phys. B, 2010, 19 (5): 050502 doi: 10.1088/1674-1056/19/5/050502
Full Text: [PDF 144 KB] (Downloads:990)
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We have investigated the thermodynamic behaviour of ideal Bose gases with an arbitrary number of particles confined in a harmonic potential. By taking into account the conservation of total number $N$ of particles and using a saddle-point approximation, we derive analytically the simple explicit expression of mean occupation number in any state of the finite system. The temperature dependence of the chemical potential, specific heat, and condensate fraction for the trapped finite-size Bose system is obtained numerically. We compare our results with the usual treatment which is based on the grand canonical ensemble. It is shown that there exists a considerable difference between them at sufficiently low temperatures, specially for the relative small numbers of Bose atoms. The finite-size scaling at the transition temperature for the harmonically trapped systems is also discussed. We find that the scaled condensate fractions for various system sizes and temperatures collapse onto a single scaled form.

Exact analytical solutions to the mean-field model depicting microcavity containing semiconductor quantum wells

Song Pei-Jun, Lü Xin-You, Liu Ji-Bing, Hao Xiang-Ying
Chin. Phys. B, 2010, 19 (5): 050503 doi: 10.1088/1674-1056/19/5/050503
Full Text: [PDF 610 KB] (Downloads:519)
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By using a two-mode mean-field approximation, we study the dynamics of the microcavities containing semiconductor quantum wells. The exact analytical solutions are obtained in this study. Based on these solutions, we show that the emission from the microcavity manifests periodic oscillation behaviour and the oscillation can be suppressed under a certain condition.

Stochastic resonance in an asymmetric bistable system driven by coloured noises

Yang Jian-Hua, Liu Xian-Bin
Chin. Phys. B, 2010, 19 (5): 050504 doi: 10.1088/1674-1056/19/5/050504
Full Text: [PDF 180 KB] (Downloads:780)
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The phenomenon of stochastic resonance is investigated in an asymmetric bistable system with coloured noises. The approximate Fokker--Planck equation is derived based on the Novikov theorem and the Fox approach. By applying the two-state theory, the expression of the signal-to-noise ratio is obtained in the adiabatic limit. The effects of the noise parameters on signal-to-ratio are discussed. It is found that the stochastic resonance phenomena appear in most cases and disappear in some special cases.

An efficient method of distinguishing chaos from noise

Wei Heng-Dong, Li Li-Ping, Guo Jian-Xiu
Chin. Phys. B, 2010, 19 (5): 050505 doi: 10.1088/1674-1056/19/5/050505
Full Text: [PDF 287 KB] (Downloads:775)
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It is an important problem in chaos theory whether an observed irregular signal is deterministic chaotic or stochastic. We propose an efficient method for distinguishing deterministic chaotic from stochastic time series for short scalar time series. We first investigate, with the increase of the embedding dimension, the changing trend of the distance between two points which stay close in phase space. And then, we obtain the differences between Gaussian white noise and deterministic chaotic time series underlying this method. Finally, numerical experiments are presented to testify the validity and robustness of the method. Simulation results indicate that our method can distinguish deterministic chaotic from stochastic time series effectively even when the data are short and contaminated.

Fault tolerant synchronization of chaotic systems based on T-S fuzzy model with fuzzy sampled-data controller

Ma Da-Zhong, Zhang Hua-Guang, WangZhan-Shan, Feng Jian
Chin. Phys. B, 2010, 19 (5): 050506 doi: 10.1088/1674-1056/19/5/050506
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In this paper the fault tolerant synchronization of two chaotic systems based on fuzzy model and sample data is investigated. The problem of fault tolerant synchronization is formulated to study the global asymptotical stability of the error system with the fuzzy sampled-data controller which contains a state feedback controller and a fault compensator. The synchronization can be achieved no matter whether the fault occurs or not. To investigate the stability of the error system and facilitate the design of the fuzzy sampled-data controller, a Takagi--Sugeno (T--S) fuzzy model is employed to represent the chaotic system dynamics. To acquire the good performance and produce less conservative analysis result, a new parameter-dependent Lyapunov--Krasovksii functional and a relaxed stabilization technique are considered. The stability conditions based on linear matrix inequality are obtained to achieve the fault tolerant synchronization of the chaotic systems. Finally, a numerical simulation is shown to verify the results.

A new approach to stability analysis of neural networks with time-varying delay via novel Lyapunov--Krasovskii functional

S. M. Lee, O. M. Kwon, Ju H. Park
Chin. Phys. B, 2010, 19 (5): 050507 doi: 10.1088/1674-1056/19/5/050507
Full Text: [PDF 103 KB] (Downloads:803)
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In this paper, new delay-dependent stability criteria for asymptotic stability of neural networks with time-varying delays are derived. The stability conditions are represented in terms of linear matrix inequalities (LMIs) by constructing new Lyapunov--Krasovskii functional. The proposed functional has an augmented quadratic form with states as well as the nonlinear function to consider the sector and the slope constraints. The less conservativeness of the proposed stability criteria can be guaranteed by using convex properties of the nonlinear function which satisfies the sector and slope bound. Numerical examples are presented to show the effectiveness of the proposed method.

Embedding adaptive arithmetic coder in chaos-based cryptography

Li Heng-Jian, Zhang Jia-Shu
Chin. Phys. B, 2010, 19 (5): 050508 doi: 10.1088/1674-1056/19/5/050508
Full Text: [PDF 147 KB] (Downloads:811)
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In this study an adaptive arithmetic coder is embedded in the Baptista-type chaotic cryptosystem for implementing secure data compression. To build the multiple lookup tables of secure data compression, the phase space of chaos map with a uniform distribution in the search mode is divided non-uniformly according to the dynamic probability estimation of plaintext symbols. As a result, more probable symbols are selected according to the local statistical characters of plaintext and the required number of iterations is small since the more probable symbols have a higher chance to be visited by the chaotic search trajectory. By exploiting non-uniformity in the probabilities under which a number of iteration to be coded takes on its possible values, the compression capability is achieved by adaptive arithmetic code. Therefore, the system offers both compression and security. Compared with original arithmetic coding, simulation results on Calgary Corpus files show that the proposed scheme suffers from a reduction in compression performance less than 12{\%} and is not susceptible to previously carried out attacks on arithmetic coding algorithms.

Dynamical analysis and experimental verification of valley current controlled buck converter

Zhou Guo-Hua, Bao Bo-Cheng, Xu Jian-Ping, Jin Yan-Yan
Chin. Phys. B, 2010, 19 (5): 050509 doi: 10.1088/1674-1056/19/5/050509
Full Text: [PDF 2551 KB] (Downloads:1157)
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The dynamical behaviours of valley current controlled buck converter are studied by establishing its corresponding discrete iterative map model in this paper. Time-domain waveforms and phase portraits of valley current controlled buck converter are obtained by Runge--Kutta algorithm through a piecewise smooth switching model. The research results indicate that the valley current controlled buck converter exhibits rich nonlinear phenomena, and it has routes to chaos through period-doubling bifurcation and border-collision bifurcation in a wide parameter range. Interesting inverse nonlinear behaviours compared with peak current controlled buck converter are observed in the valley current controlled buck converter. Analysis and simulation results are verified by experimental results.

Filtering noisy chaotic signal via sparse representation based on random frame dictionary

Xie Zong-Bo, FengJiu-Chao
Chin. Phys. B, 2010, 19 (5): 050510 doi: 10.1088/1674-1056/19/5/050510
Full Text: [PDF 136 KB] (Downloads:593)
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The denoising problem of impure chaotic signals is addressed in this paper. A method based on sparse representation is proposed, in which the random frame dictionary is generated by a chaotic random search algorithm. The numerical simulation shows the proposed algorithm outperforms those recently reported alternative denoising methods.

Random-phase-induced chaos in power systems

Qin Ying-Hua, Luo Xiao-Shu, WeiDu-Qu
Chin. Phys. B, 2010, 19 (5): 050511 doi: 10.1088/1674-1056/19/5/050511
Full Text: [PDF 383 KB] (Downloads:582)
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This paper studies how random phase (namely, noise-perturbed phase) effects the dynamical behaviours of a simple model of power system which operates in a stable regime far away from chaotic behaviour in the absence of noise. It finds that when the phase perturbation is weak, chaos is absent in power systems. With the increase of disturbed intensity $\sigma$, power systems become unstable and fall into chaos as $\sigma$ further increases. These phenomena imply that random phase can induce and enhance chaos in power systems. Furthermore, the possible mechanism behind the action of random phase is addressed.

Control and synchronization of second Julia sets

Zhang Yong-Ping, Sun Wei-Hua, Liu Chang-An
Chin. Phys. B, 2010, 19 (5): 050512 doi: 10.1088/1674-1056/19/5/050512
Full Text: [PDF 894 KB] (Downloads:960)
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A visualization of Julia sets of the complex Henon map system with two complex variables is introduced in this paper. With this method, the optimal control function method is introduced to this system and the control and synchronization of its Julia sets are achieved. Control and synchronization of generalized Julia sets are also achieved with this optimal control method. The simulations illustrate the efficacy of this method.

Doppler instability of antispiral waves in discrete oscillatory reaction-diffusion media

Qian Yu, Huang Xiao-Dong, Liao Xu-Hong, Hu Gang
Chin. Phys. B, 2010, 19 (5): 050513 doi: 10.1088/1674-1056/19/5/050513
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This paper investigates antispiral wave breakup phenomena in coupled two-dimensional FitzHugh--Nagumo cells with self-sustained oscillation via Hopf bifurcation. When the coupling strength of the active variable decreases to a critical value, wave breakup phenomenon first occurs in the antispiral core region where waves collide with each other and spontaneously break into spatiotemporal turbulence. Measurements reveal for the first time that this breakup phenomenon is due to the mechanism of antispiral Doppler instability.

Distributed predictive control of spiral wave in cardiac excitable media

Gan Zheng-Ning, Cheng Xin-Ming
Chin. Phys. B, 2010, 19 (5): 050514 doi: 10.1088/1674-1056/19/5/050514
Full Text: [PDF 986 KB] (Downloads:425)
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In this paper, we propose the distributed predictive control strategies of spiral wave in cardiac excitable media. The modified FitzHugh--Nagumo model was used to express the cardiac excitable media approximately. Based on the control-Lyapunov theory, we obtained the distributed control equation, which consists of a positive control-Lyapunov function and a positive cost function. Using the equation, we investigate two kinds of robust control strategies: the time-dependent distributed control strategy and the space-time dependent distributed control strategy. The feasibility of the strategies was demonstrated via an illustrative example, in which the spiral wave was prevented to occur, and the possibility for inducing ventricular fibrillation was eliminated. The strategies are helpful in designing various cardiac devices. Since the second strategy is more efficient and robust than the first one, and the response time in the second strategy is far less than that in the first one, the former is suitable for the quick-response control systems. In addition, our spatiotemporal control strategies, especially the second strategy, can be applied to other cardiac models, even to other reaction-diffusion systems.

Reflection and refraction of waves in oscillatory media

Gu Guo-Feng, L\"u Yao-Ping, Tang Guo-Ning
Chin. Phys. B, 2010, 19 (5): 050515 doi: 10.1088/1674-1056/19/5/050515
Full Text: [PDF 1084 KB] (Downloads:573)
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This paper uses the two-dimensional Brusselator model to study reflection and refraction of chemical waves. It presents some boundary conditions of chemical waves, with which occurence of observed phenomena at interface as refraction and reflection of chemical waves can be interpreted. Moreover, the angle of reflection may be calculated by using the boundary conditions. It finds that reflection and refraction of chemical waves can occur simultaneously even if plane wave goes from a medium with higher speed to a medium with lower speed, provided the incident angle is larger than the critical angle.

Intermittencies in complex Ginzburg-Landau equation by varying system size

Li Hai-Hong, Xiao Jing-Hua, Hu Gang, HuBambi
Chin. Phys. B, 2010, 19 (5): 050516 doi: 10.1088/1674-1056/19/5/050516
Full Text: [PDF 3849 KB] (Downloads:690)
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Dynamical behaviour of the one-dimensional complex Ginzburg--Landau equation (CGLE) with finite system size $L$ is investigated, based on numerical simulations. By varying the system size and keeping other system parameters in the defect turbulence region (defect turbulence in large $L$ limit), a number of intermittencies new for the CGLE system are observed in the processes of pattern formations and transitions while the system dynamics varies from a homogeneous periodic oscillation to strong defect turbulence.

Effects of the number of on-rampson the ring traffic flow

Tang Tie-Qiao, Huang Hai-Jun, Shang Hua-Yan
Chin. Phys. B, 2010, 19 (5): 050517 doi: 10.1088/1674-1056/19/5/050517
Full Text: [PDF 978 KB] (Downloads:745)
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Since ramp is an important composition of traffic system and there often exist multi ramps in a traffic system, the number of ramps can have great effects on main road traffic and produce some complex phenomena. In this paper, we employ the model presented by Tang \textit{et al}. [2009 {\em Communications in Theoretical Physics} {\bf 51}({1}) 71] to further study the effects of the number of on-ramps on the stability of traffic flow on a ring road. The numerical results show that this model can reproduce some complex traffic phenomena resulting from multi on-ramps on the ring road and the effects of the number of on-ramps on traffic flow, but the phenomena and the effects are both related to the initial density of the main road.

Kinetic Ising model in a time-dependent oscillating external magnetic field: effective-field theory

Bayram Deviren, Osman Canko, Mustafa Keskin
Chin. Phys. B, 2010, 19 (5): 050518 doi: 10.1088/1674-1056/19/5/050518
Full Text: [PDF 1485 KB] (Downloads:760)
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Recently, Shi {\it et al.} [2008 {\it Phys. Lett.} A {\bf372} 5922] have studied the dynamical response of the kinetic Ising model in the presence of a sinusoidal oscillating field and presented the dynamic phase diagrams by using an effective-field theory (EFT) and a mean-field theory (MFT). The MFT results are in conflict with those of earlier work of Tom\'{e} and de Oliveira, [1990 {\it Phys. Rev.} A {\bf41} 4251]. We calculate the dynamic phase diagrams and find that our results are similar to those of earlier work of Tom\'{e} and de Oliveira; hence the dynamic phase diagrams calculated by Shi {\it et al.} are incomplete within both theories, except the low values of frequencies for the MFT calculation. We also investigate the influence of external field frequency ($\omega$) and static external field amplitude ($h_{0})$ for both MFT and EFT calculations. We find that the behaviour of the system strongly depends on values of $\omega$ and $h_{0}$.

Shot noise in electron transport through a double quantum dot: a master equation approach

Ou-Yang Shi-Hua, Lam Chi-Hang, You Jian-Qiang
Chin. Phys. B, 2010, 19 (5): 050519 doi: 10.1088/1674-1056/19/5/050519
Full Text: [PDF 572 KB] (Downloads:834)
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We study shot noise in tunneling current through a double quantum dot connected to two electric leads. We derive two master equations in the occupation-state basis and the eigenstate basis to describe the electron dynamics. The approach based on the occupation-state basis, despite being widely used in many previous studies, is valid only when the interdot coupling strength is much smaller than the energy difference between the two dots. In contrast, the calculations using the eigenstate basis are valid for an arbitrary interdot coupling. Using realistic model parameters, we demonstrate that the predicted currents and shot-noise properties from the two approaches are significantly different when the interdot coupling is not small. Furthermore, properties of the shot noise predicted using the eigenstate basis successfully reproduce qualitative features found in a recent experiment.

Consensus problems in multi-agent systems with double integrator model

Gao Li-Xin, Yan Hui-Juan, Jin Dan
Chin. Phys. B, 2010, 19 (5): 050520 doi: 10.1088/1674-1056/19/5/050520
Full Text: [PDF 387 KB] (Downloads:695)
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In this paper, we consider multi-agent consensus problems in a decentralised fashion. The interconnection topology graph among the agents is switching and undirected. The agent dynamics is expressed in the form of a double integrator model. Two different cases are considered in this study. One is the leader-following case and the other is leaderless case. Based on graph theory and common Lyapunov function method, some sufficient conditions are obtained for the consensus stability of the considered systems with the neighbour-based feedback laws in both leader-following case and leaderless case respectively. Finally, two numerical examples are given to illustrate the obtained results.

Theory of higher harmonics imaging in tapping-mode atomic force microscopy

Li Yuan, Qian Jian-Qiang, Li Ying-Zi
Chin. Phys. B, 2010, 19 (5): 050701 doi: 10.1088/1674-1056/19/5/050701
Full Text: [PDF 154 KB] (Downloads:509)
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The periodic impact force induced by tip-sample contact in tapping mode atomic force microscope (AFM) gives rise to non-harmonic response of a micro-cantilever. These non-harmonic signals contain the full characteristics of tip-sample interaction. A complete theoretical model describing the dynamical behaviour of tip--sample system was developed in this paper. An analytic formula was introduced to describe the relationship between time-varying tip--sample impact force and tip motion. The theoretical analysis and numerical results both show that the time-varying tip--sample impact force can be reconstructed by recording tip motion. This allows for the reconstruction of the characteristics of the tip--sample force, like contact time and maximum contact force. It can also explain the ability of AFM higher harmonics imaging in mapping stiffness and surface energy variations.
CLASSICAL AREAS OF PHENOMENOLOGY

Investigation on global positioning system signal scattering and propagation over the rough sea surface

Yang Chao, Guo Li-Xin, Wu Zhen-Sen
Chin. Phys. B, 2010, 19 (5): 054101 doi: 10.1088/1674-1056/19/5/054101
Full Text: [PDF 347 KB] (Downloads:748)
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This paper is devoted to the study of polarization properties, scattering properties and propagation properties of global positioning system (GPS) scattering signal over the rough sea surface. To investigate the polarization and the scattering properties, the scattering field and the bistatic scattering coefficient of modified Kirchhoff approximation with using the tapered incident wave is derived in detail. In modeling the propagation properties of the GPS scattering signal in the evaporation duct, the initial field of parabolic equation traditionally computed by the antenna pattern with using fast Fourier transform (FFT) is replaced by the GPS scattering field. And the propagation properties of GPS scattering signal in the evaporation duct with different evaporation duct heights and elevation angles of GPS are discussed by the improved discrete mixed Fourier transform with taking into account the sea surface roughness.

Electromagnetic backscattering from freak waves in(1+1)-dimensional deep-water

Xie Tao, Shen Tao, William Perrie, Chen Wei, Kuang Hai-Lan
Chin. Phys. B, 2010, 19 (5): 054102 doi: 10.1088/1674-1056/19/5/054102
Full Text: [PDF 941 KB] (Downloads:709)
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To study the electromagnetic (EM) backscatter characteristics of freak waves at moderate incidence angles, we establish an EM backscattering model for freak waves in (1+1)-dimensional deep water. The nonlinear interaction between freak waves and Bragg short waves is considered to be the basic hydrodynamic spectra modulation mechanism in the model. Numerical results suggest that the EM backscattering intensities of freak waves are less than those from the background sea surface at moderate incidence angles. The normalised radar cross sections (NRCSs) from freak waves are highly polarisation dependent, even at low incidence angles, which is different from the situation for normal sea waves; moreover, the NRCS of freak waves is more polarisation dependent than the background sea surface. NRCS discrepancies between freak waves and the background sea surface with using horizontal transmitting horizomtal (HH) polarisation are larger than those with using vertical transmitting vertical (VV) polarisation, at moderate incident angles. NRCS discrepancies between freak waves and background sea surface decreases with the increase of incidence angle, in both HH and VV polarisation radars. As an application, in the synthetic-aperture radar (SAR) imaging of freak waves, we suggest that freak waves should have extremely low backscatter NRCSs for the freak wave facet with the strongest slope. Compared with the background sea surface, the freak waves should be darker in HH polarisation echo images than in VV echo images, in SAR images. Freak waves can be more easily detected from the background sea surface in HH polarisation images than in VV polarisation images. The possibility of detection of freak waves at low incidence angles is much higher than at high incidence angles.

Study of scattering from time-varying Gerstners sea surface using second-order small slope approximation

Zhang Yan-Min, Wang Yun-Hua, Guo Li-Xin
Chin. Phys. B, 2010, 19 (5): 054103 doi: 10.1088/1674-1056/19/5/054103
Full Text: [PDF 1802 KB] (Downloads:676)
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Backscattered fields from one-dimensional time-varying Gerstners sea surface are calculated utilising the second-order small slope approximation. It is well known that spectral properties of the backscattered echoes relate to the velocity of the small elementary scatterers on sea surface profiles. Therefore, modeling Doppler spectra from the ocean requires an accurate description of the sea surface motion. The profile of nonlinear Gerstners sea surface shows vertical-skewness of sea waves, it is sharper at the crest and flatter at the trough than linear waves, and its maximum slope position is closer to the crest than to the trough. Furthermore, the horizontal component of the small elementary scatterers orbit velocity on the sea surface, which yields noticeable influence on Doppler spectra, can be obtained conveniently by Gerstners sea surface model. In this study, the characteristics of Doppler spectra of backscattered fields from time-varying Gerstners sea surface are investigated and the dependences of the Doppler frequency and the Doppler bandwidth on the parameters, such as the wind speed, the radar frequency, the incident angle, etc. are discussed. It is shown that the Doppler bandwidth of microwave scattered fields from Gerstners sea surface is considerably broadened. For the case of high frequency backscattered fields, the values of the higher-order spectrum peaks are larger than those obtained by linear sea surface.

Numerical analysis of surface plasmon nanocavities formed inthickness-modulated metal-insulator-metal waveguides

Liu Jian-Long, Lin Jie, Zhao Hai-Fa, Zhang Yan, Liu Shu-Tian
Chin. Phys. B, 2010, 19 (5): 054201 doi: 10.1088/1674-1056/19/5/054201
Full Text: [PDF 252 KB] (Downloads:1286)
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The enhancement characteristics of the local field in the surface plasmon nanocavities are investigated numerically. The cavity is constructed by placing a defect structure in the thickness-modulated metal--insulator--metal waveguide Bragg gratings. The characteristic impedance based transfer matrix method is used to calculate the transmission spectra and the resonant wavelength of the cavities with various geometric parameters. The finite-difference time-domain method is used to obtain the field pattern of the resonant mode and validate the results of the transfer matrix method. The calculation and simulation results reveal the existence of resonant wavelength shift and intensity variation with structural parameters, such as the modulation period of the gratings, the length and the width of the defect structure. Both numerical analysis and theoretical interpretation on these phenomena are given in details.

Study on guided-mode resonance characteristic of multilayer dielectric grating with broadband and wide using-angle

Wang Jian-Peng, Jin Yun-Xia, MaJian-Yong, Shao Jian-Da, Fan Zheng-Xiu
Chin. Phys. B, 2010, 19 (5): 054202 doi: 10.1088/1674-1056/19/5/054202
Full Text: [PDF 4999 KB] (Downloads:1134)
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Guided-mode resonance in a diffraction band of multilayer dielectric gratings may lead to a catastrophic result in laser system, especially in the ultrashort pulse laser system, so the inhibition of guided-mode resonance is very important. In this paper the characteristics of guided-mode resonance in multilayer dielectric grating are studied with the aim of better understanding the physical process of guided-mode resonance and designing a broadband multilayer dielectric grating with no guided-mode resonance. By employing waveguide theory, all guided-wave modes appearing in multilayer dielectric grating are found, and the incident conditions, separately, corresponding to each guided-wave mode are also obtained. The electric field enhancement in multilayer dielectric grating is shown obviously. Furthermore, from the detailed analyses on the guided-mode resonance conditions, it is found that the reduction of grating period would effectively avoid the appearing of guided-mode resonance. And the expressions for calculating maximum periods, which ensure that no guided-mode resonance occurs in the requiring broad angle or wavelength range, are first reported. The above results calculated by waveguide theory and Fourier mode method are compared wit each other, and they are coincident completely. Moreover, the method that relies on waveguide theory is more helpful for understanding the guided-mode resonance excited process and analyzing how each parameter affects the characteristic of guided-mode resonance. Therefore, the effects of multilayer dielectric grating parameters, such as period, fill factor, thickness of grating layer, {\it et al.}, on the guided-mode resonance characteristic are discussed in detail based on waveguide theory, and some meaningful results are obtained.

Stokes parameters of optical singularities of random electromagnetic beams

Li Jian-Long, Zhu Shi-Fu
Chin. Phys. B, 2010, 19 (5): 054203 doi: 10.1088/1674-1056/19/5/054203
Full Text: [PDF 438 KB] (Downloads:620)
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In this paper, the relation between spectral degree of coherence and degree of polarization of random electromagnetic beams is derived by the Stokes parameters. And the concept of polarization singularity is extended from spatially fully coherent beams to partially coherent electromagnetic beams. Theoretical analysis shows that correlation vortices are linearly polarized singularities. The results are illustrated by numerical examples.

Phase properties of odd and even circular states

Wang Yue-Yuan, Liu Zheng-Jun, Liao Qing-Hong, Liu Shu-Tian
Chin. Phys. B, 2010, 19 (5): 054204 doi: 10.1088/1674-1056/19/5/054204
Full Text: [PDF 1269 KB] (Downloads:623)
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Phase properties of the even and odd circular states are studied within the Hermitian phase formalism of Pegg and Barnett. Exact analytical formulas for the distribution function and the variance of the phase operator are obtained and used to examine whether or not the even and odd circular states exhibit photon-number squeezing and phase squeezing.

Steady-state analysis of three-photon absorption spectra via density-matrix method in a three-coupled-quantum-well nanostructure

Deng Li
Chin. Phys. B, 2010, 19 (5): 054205 doi: 10.1088/1674-1056/19/5/054205
Full Text: [PDF 1055 KB] (Downloads:819)
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We numerically simulate three-photon absorption spectra in a three-coupled-quantum-well nanostructure interacting with a pump field, a coherent coupling field, and a probe field. We find that the three-photon absorption spectra can be dramatically influenced due to the intensities of the coupling field and pump field changing under the three-photon resonance condition. The effect of the frequency detuning of the pump field on the three-photon absorption spectra is also discussed. The study in our case is much more practical than the study in the case of its atomic counterpart in the sense of flexible design and the wide adjustable parameters. Thus it may open up some new possibilities for technological applications in optoelectronics and solid-state quantum information science.

Phase control of spontaneous emission from a double-band photonic crystals

Zhang Ke, Zhu Yan-Ping, Jiang Li, Zhang Han-Zhuang
Chin. Phys. B, 2010, 19 (5): 054206 doi: 10.1088/1674-1056/19/5/054206
Full Text: [PDF 160 KB] (Downloads:759)
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Through picture of dressed states, this paper investigates the spontaneous emission spectrum from a microwave-driven three-level atom embedded in a double-band photonic crystals. The physical dynamics of the phase dependent phenomenon is analysed by comparing two models `upper level coupling' and `lower level coupling'. When the phase is changed from 0 to $\pi$, the variety of spontaneous emission spectra from either of the two models are inverse to each other, in which the relative height and width of peaks are determined by the density of states in photonic crystals.

Linearly polarised three-colour lasing emission from an evanescent wave pumped and gain coupled fibre laser

Pu Xiao-Yun, Jiang Nan, Han De-Yu, Feng Yong-Li, Ren Yi-Tao
Chin. Phys. B, 2010, 19 (5): 054207 doi: 10.1088/1674-1056/19/5/054207
Full Text: [PDF 2107 KB] (Downloads:652)
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A novel Whispering--Gallery--Mode (WGM) fibre laser, emitting linearly polarised three-colour light, is demonstrated by pumping and gain coupling with evanescent waves. The pump light is longitudinally coupled into a bare optical fibre immersed in a dye solution of lower refractive index. The dye molecules around the bare fibre are excited by the evanescent waves of pump light when they propagate along the fibre in a total internal reflection. When the pump beam within the fibre is a meridian beam, the WGM lasing emission from the fibre laser is a linearly polarised transverse electric wave, while it is a mixed wave of the linearly polarised transverse electric and magnetic waves if the pump beam is a skew beam within the fibre. Because the excited molecules are located within the evanescent field of WGM, a good spatial overlap between the dye gain and the evanescent field leads to a high pumping efficiency and a longer gain distance along the fibre. Once the bare fibre is inserted into three glass capillaries filled with Rhodamine 6G, 610 and 640 dye solutions, respectively, WGM laser oscillations at the wavelengths of 567--575, 605--614 and 656--666~nm occur simultaneously, and a linearly polarised three-colour lasing emission is achieved in a single optical fibre.

Design of surface emitting distributed feedback quantum cascade laser with single-lobe far-field pattern and high outcoupling efficiency

Guo Wan-Hong, Liu Jun-Qi, Lu Quan-Yong, Zhang Wei, Li Lu, Wang Li-Jun, Liu Feng-Qi, Wang Zhan-Guo
Chin. Phys. B, 2010, 19 (5): 054208 doi: 10.1088/1674-1056/19/5/054208
Full Text: [PDF 323 KB] (Downloads:1260)
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A 7.8-$\mu $m surface emitting second-order distributed feedback quantum cascade laser (DFB QCL) structure with metallized surface grating is studied. The modal property of this structure is described by utilizing coupled-mode theory where the coupling coefficients are derived from exact Floquet--Bloch solutions of infinite periodic structure. Based on this theory, the influence of waveguide structure and grating topography as well as device length on the laser performance is numerically investigated. The optimized surface emitting second-order DFB QCL structure design exhibits a high surface outcoupling efficiency of 22{\%} and a low threshold gain of 10~cm$^{ - 1}$. Using a {$\pi $} phase-shift in the centre of the grating, a high-quality single-lobe far-field radiation pattern is obtained.

Efficient corner-pumped Nd:YAG/YAG composite slab laser

Liu Huan, Gong Ma-Li
Chin. Phys. B, 2010, 19 (5): 054209 doi: 10.1088/1674-1056/19/5/054209
Full Text: [PDF 1723 KB] (Downloads:1042)
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A corner-pumped type is a new pumping type in the diode-pumped all-solid-state lasers, which has the advantages of high pump efficiency and favourable pump uniformity. A highly efficient corner-pumped Nd:YAG/YAG composite slab laser is demonstrated in this paper. The maximal continuous-wave output power of the 1064~nm laser is up to 18.57~W with a slope efficiency and an optical-to-optical conversion efficiency of 44.9{\%} and 39.8{\%}, respectively. Inserting an acousto-optic $Q$-switch in the cavity, the highest average output power of the quasi-continuous wave 1064~nm laser of 6.73~W is obtained at a repetition rate of 9.26~kHz. The experimental results show that a corner-pumped type is a kind of feasible schedules in the design of diode-pumped all-solid-state lasers with low or medium output powers.

Femtosecond laser-induced microstructure in Foturan glass

Sun Hai-Yi, Luo Fang-Fang, HeFei, Liao Yang, Xu Jian
Chin. Phys. B, 2010, 19 (5): 054210 doi: 10.1088/1674-1056/19/5/054210
Full Text: [PDF 3037 KB] (Downloads:1227)
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We report on the microstructure formation in Foturan glass, induced by 1~kHz, 120 femtosecond laser irradiation. It is found that the line-shaped filamentation, not void array tends to be formed in this glass. This is different from our previous experimental results in fused silica and BK7 glasses. A possible mechanism Ag$^+$ captures the free electrons generated by laser, is proposed to explain the observed phenomena.

The propagation of dipole solitonsin highly nonlocal medium

Zhao Jia-Yin, Wang Qi, Shen Ming, Shi Jie-Long, Kong Qian, Ge Li-Juan
Chin. Phys. B, 2010, 19 (5): 054211 doi: 10.1088/1674-1056/19/5/054211
Full Text: [PDF 182 KB] (Downloads:875)
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This paper studies the propagation of dipole solitons in highly nonlocal medium by using the variational method. It finds that the dipole solitons will be stable when the input power obeys a restrict value. When the incident power does not satisfy the stable conditions, the nonlocal accessible dipole solitons will undergo linear harmonic oscillation. It shows such evolution behaviours in detail.

High energy and long pulse generation with high-birefringence photonic crystal fibre and laser-diode pumped regenerative amplifier

Wang He-Lin, Wang Cheng, Leng Yu-Xin, Xu Zhi-Zhan, Hou Lan-Tian
Chin. Phys. B, 2010, 19 (5): 054212 doi: 10.1088/1674-1056/19/5/054212
Full Text: [PDF 1094 KB] (Downloads:919)
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We report on the generation of a high energy and long pulse for pumping optical parametric chirped-pulse amplification (OPCPA) by a high-birefringence photonic crystal fibre (HB-PCF) and a laser-diode-pumped regenerative chirped pulse amplifier. Using the femtosecond pump pulse centred at 815~nm, a 1064~nm soliton pulse is produced in the HB-PCF. After injecting it into an Nd:YAG regenerative amplifier with the glass etalons, a narrow-band amplified pulse with an energy of $\sim $4~mJ and a duration of 235 ps is achieved at a repetition rate of 10~Hz, which is suitable for being used as a pump source in the 800~nm OPCPA system.

Separate holographic screening soliton pairs in a biased series photorefractive crystal circuit

Cai Xin, Liu Jin-Song, Lü Jian-Tao
Chin. Phys. B, 2010, 19 (5): 054213 doi: 10.1088/1674-1056/19/5/054213
Full Text: [PDF 590 KB] (Downloads:628)
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Holographic dark (bright) screening solitons are predicted in one dimension for a series circuit consisting of two photorefractive crystals connected electronically by electrode leads in a chain with a voltage source. Each crystal can support a holographic screening soliton. The two solitons are known collectively as a separate holographic screening soliton pair with three types: bright--bright, bright--dark and dark--dark. The numerical results show that the two solitons in a soliton pair can affect each other through a light-induced current and their coupling can affect their spatial profiles under the limit in which the optical wave has a spatial extent much less than the width of the crystal.

Ultraslow optical solitons via electromagnetically induced transparency: a density-matrix approach

Luo Bin, Hang Chao, Li Hui-Jun, Huang Guo-Xiang
Chin. Phys. B, 2010, 19 (5): 054214 doi: 10.1088/1674-1056/19/5/054214
Full Text: [PDF 189 KB] (Downloads:896)
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We study the ultraslow optical solitons in a resonant three-level atomic system via electromagnetically induced transparency under a density-matrix (DM) approach. The results of linear and nonlinear optical properties are compared with those obtained by using an amplitude variable (AV) approach. It is found that the results for both approaches are the same in the linear regime if the corresponding relations between the population-coherence decay rates in the DM approach and the energy-level decay rates in the AV approach are appropriately imposed. However, in the nonlinear regime there is a small difference for the self-phase modulation coefficient of the nonlinear Schr\"{o}dinger equation that governs the time evolution of probe pulse envelope. All analytical predicts are checked by numerical simulations.

Relationship between group velocity and symmetry of photonic crystals

Ye Wei-Min, Luo Zhang, Yuan Xiao-Dong, Zeng Chun
Chin. Phys. B, 2010, 19 (5): 054215 doi: 10.1088/1674-1056/19/5/054215
Full Text: [PDF 291 KB] (Downloads:661)
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Group velocity (GV) of eigenmode is a crucial parameter to explain the extraordinary phenomena about light propagation in photonic crystals (PhCs). To study relationships between group velocity and symmetry of PhCs, a new general expression of GV in PhCs made up of non-dispersive material is introduced. Based on this, the GVs of eigenmodes of PhCs, especially those of degenerate eigenmodes at highly symmetric points in the first Brillouin zone, are discussed. Some interesting results are obtained. For example, the summation of degenerate eigenmodes' GVs is invariant under the operations of wave vector ${{\bm K}}$-group $M_{{\bm K}} $. In addition, some numerical results are presented to verify them.

Physical model of acoustic forward scattering by cylindrical shell and its experimental validation

Lei Bo, Yang Kun-De, MaYuan-Liang
Chin. Phys. B, 2010, 19 (5): 054301 doi: 10.1088/1674-1056/19/5/054301
Full Text: [PDF 4660 KB] (Downloads:1107)
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Research on the underwater target scattering can provide important theoretical support for target detection. The scattering model of cylindrical shell is established in this paper. It is found that the forward target strength is much stronger and varies with angles of incident wave less significantly than backward target strength. The received forward signal strength fluctuates with the target moving due to the interference between direct signal and scattering signal, which is most significant when target approaches the baseline. An experiment is carried out in an anechoic tank to validate the scattering model. The method of acquisiting forward scattering in the tank is proposed. The forward and the backward target strengths are achieved by using the pulse compression technology, and they are about 3dB less than the modeling results. The forward scattering phenomena of quiescent and moving target are measured, which are similar to modeling results with different target types.

Finite element modeling of acoustic scattering from an encapsulated microbubble near rigid boundary

Huang Bei, Zhang Yan-Li, Zhang Dong, Gong Xiu-Fen
Chin. Phys. B, 2010, 19 (5): 054302 doi: 10.1088/1674-1056/19/5/054302
Full Text: [PDF 642 KB] (Downloads:1123)
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This article proposes a finite element model (FEM) for predicting the acoustic scattering from an encapsulated microbubble near rigid boundary. The validity of the model is first examined by comparing the acoustic nonlinear response of a free microbubble with that obtained by the Church model. Then this model is used to investigate the effect of the rigid boundary on acoustic scattering signals from microbubble. The results indicate that the resonance frequency decreases while the oscillation amplitude increases as the microbubble approaches the rigid boundary. In addition, the fundamental component of the acoustic scattering signal is enhanced compared with that of the free microbubble.

Analysis and improvement of sound radiation performance of spherical cap radiator

Tang Yi-Zheng, Wu Zhao-Jun, Tang Li-Guo
Chin. Phys. B, 2010, 19 (5): 054303 doi: 10.1088/1674-1056/19/5/054303
Full Text: [PDF 317 KB] (Downloads:583)
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A spherical cap radiator is one of the important parts of an underwater wide-beam imaging system. The back radiation of a traditional spherical cap radiator, which is composed of a vibrating cap and a rigid baffle, is strong and its far-field directivity function may fluctuate in big amplitude in the vicinity of the polar axis. These shortcomings complicate the processing of the reflective waves received for imaging the targets. In this study, the back radiation is weakened by adding an acoustic soft material belt between the vibrating cap and the rigid baffle. And the fluctuation mentioned above is lowered remarkably by dividing the spherical cap radiator into many annuluses and a relatively smaller spherical cap, and by controlling the phase retardations of all elements appropriately. Furthermore, the numerical experiments are carried out by the finite element method (FEM) to prove the validity of the above methods.

Anomalous energy diffusion and heat conduction in one-dimensional system

Li Hai-Bin, Li Zhen
Chin. Phys. B, 2010, 19 (5): 054401 doi: 10.1088/1674-1056/19/5/054401
Full Text: [PDF 184 KB] (Downloads:568)
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We propose a new concept, the centre of energy, to study energy diffusion and heat conduction in one-dimensional hard-point model. For diatom model, we find an anomalous energy diffusion as $\langle x^2 \rangle\sim t^\beta$ with $\beta=1.33$, which is independent of initial condition and mass rate. The present model can be viewed as the model composed by independent quasi-particles, the centre of energy. In this way, heat current can be calculated. Based on theory of dynamic billiard, the divergent exponent of heat conductivity is estimated to be $\alpha=0.33$, which is confirmed by a simple numerical calculation.
ATOMIC AND MOLECULAR PHYSICS

Electric-dipole allowed (E1) and forbidden (E2, M1 and M2)transition probabilities of 4f for N+

Shen Xiao-Zhi, Yuan Ping, Liu Juan
Chin. Phys. B, 2010, 19 (5): 053101 doi: 10.1088/1674-1056/19/5/053101
Full Text: [PDF 94 KB] (Downloads:741)
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By applying systematically enlarged multi-configuration Dirac--Fock wavefunction, the transitions for electric-dipole allowed (E1) and forbidden (E2, M1 and M2) lines are studied among 4f pair coupling and low-lying configurations for singly ionized nitrogen. Most important effects of relativity, electron correlation, the rearrangement of electron density, Breit interaction, and quantum electrodynamic effects are included in the computation. Then, allowed (E1) and forbidden (E2, M1 and M2) transition probabilities of 4f for N$^{+}$ are obtained and compared with experimental results. Good agreement with available experimental results is found and most of data of 4f are presented for the first time.

Study on spectroscopic parameters and molecular constants of HCl(X1+) molecule by using multireference configuration interaction approach

Zhang Xiao-Niu, Shi De-Heng, Zhang Jin-Ping, Zhu Zun-Lüe, Sun Jin-Feng
Chin. Phys. B, 2010, 19 (5): 053401 doi: 10.1088/1674-1056/19/5/053401
Full Text: [PDF 223 KB] (Downloads:1171)
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Equilibrium internuclear separations, harmonic frequencies and potential energy curves (PECs) of HCl($X^{1}\Sigma ^{ + })$ molecule are investigated by using the highly accurate valence internally contracted multireference configuration interaction (MRCI) approach in combination with a series of correlation-consistent basis sets in the valence range. The PECs are all fitted to the Murrell--Sorbie function, and they are used to accurately derive the spectroscopic parameters ($D_{\rm e}$, $D_{0}$, $\omega_{\rm e}\chi_{\rm e}$, $\alpha_{\rm e}$ and $B_{\rm e})$. Compared with the available measurements, the PEC obtained at the basis set, aug-cc-pV5Z, is selected to investigate the vibrational manifolds. The constants $D_{0}$, $D_{\rm e}$, $R_{\rm e}$, $\omega_{\rm e}$, $\omega_{\rm e}\chi_{\rm e}$, $\alpha_{\rm e}$ and $B_{\rm e}$ at this basis set are 4.4006~eV, 4.5845~eV, 0.12757~nm, 2993.33~cm$^{ - 1}$, 52.6273~cm$^{ - 1}$, 0.2981~cm$^{ - 1}$ and 10.5841~cm$^{ - 1}$, respectively, which almost perfectly conform to the available experimental results. With the potential determined at the MRCI/aug-cc-pV5Z level of theory, by numerically solving the radial Schr\"{o}dinger equation of nuclear motion in the adiabatic approximation, a total of 21 vibrational levels are predicted. Complete vibrational levels, classical turning points, inertial rotation and centrifugal distortion constants are reproduced, which are in excellent agreement with the available Rydberg--Klein--Rees data. Most of these theoretical vibrational manifolds are reported for the first time to the best of our knowledge.

Four-level model of ion-ion laser-induced collisional energy transfer and numerical calculations for Ca+-Sr+ system

Chen De-Ying, Zhang Hong-Ying, Fan Rong-Wei
Chin. Phys. B, 2010, 19 (5): 053402 doi: 10.1088/1674-1056/19/5/053402
Full Text: [PDF 167 KB] (Downloads:675)
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The four-level model of laser-induced collisional energy transfer (LICET) for ion--ion collision system is established based on the time-dependent Schr\"{o}dinger equation for the electron dynamics, through which the equations of motion of the probability amplitudes and cross section of the collision system are obtained. Numerical calculations are performed for the Ca$^+$--Sr$^+$ system, with the results showing that the peak of the LICET spectrum appears at a resonant frequency of the transfer laser. The magnitude of the obtained collision cross section is in the order of $10^{-16}$~cm$^2$, and is comparable to that obtained in atomic systems, which indicates the validity of the established four-level model.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

Generation of fast protons in moderate-intensity laser-plasma interaction from rear sheath

Tan Zhi-Xin, Huang Yong-Sheng, Lan Xiao-Fei, Lu Jian-Xin, Duan Xiao-Jiao, Wang Lei-Jian, Yang Da-Wei, Guo Shi-Lun, Wang Nai-Yan
Chin. Phys. B, 2010, 19 (5): 055201 doi: 10.1088/1674-1056/19/5/055201
Full Text: [PDF 398 KB] (Downloads:719)
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Forward fast protons are generated by the moderate-intensity laser--foil interaction. Protons with maximum energy 190~keV are measured by using magnetic spectrometer and CR-39 solid state track detectors along the direction normal to the rear surface. The experimental results are also modeled by the particle-in-cell method, investigating the time-varying electron temperature and the rear sheath field. The temporal and spatial structure of the sheath electrical field, revealed in the simulation, suggests that these protons are accelerated by target normal sheath acceleration (TNSA) mechanism.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

Influence of reducing anneal on the ferromagnetism in single crystalline Co-doped ZnO thin films

Lu Zhong-Lin, Zou Wen-Qin, Xu Ming-Xiang, ZhangFeng-Ming
Chin. Phys. B, 2010, 19 (5): 056101 doi: 10.1088/1674-1056/19/5/056101
Full Text: [PDF 928 KB] (Downloads:1160)
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This paper reports that the high-quality Co-doped ZnO single crystalline films have been grown on $a$-plane sapphire substrates by using molecular-beam epitaxy. The as-grown films show high resistivity and non-ferromagnetism at room temperature, while they become good conductive and ferromagnetic after annealing in the reducing atmosphere either in the presence or absence of Zn vapour. The x-ray absorption studies indicate that all Co ions in these samples actually substituted into the ZnO lattice without formatting any detectable secondary phase. Compared with weak ferromagnetism (0.16~$\mu _{\rm B}$/Co$^{2 + })$ in the Zn$_{0.95}$Co$_{0.05}$O single crystalline film with reducing annealing in the absence of Zn vapour, the films annealed in the reducing atmosphere with Zn vapour are found to have much stronger ferromagnetism (0.65~$\mu _{\rm B}$/Co$^{2 + })$ at room temperature. This experimental studies clearly indicate that Zn interstitials are more effective than oxygen vacancies to activate the high-temperature ferromagnetism in Co-doped ZnO films, and the corresponding ferromagnetic mechanism is discussed.

Elastic behaviour of a wedge disclination dipole near a sharp crack emanating from a semi-elliptical blunt crack

Song Hao-Peng, Fang Qi-Hong, Liu You-Wen
Chin. Phys. B, 2010, 19 (5): 056102 doi: 10.1088/1674-1056/19/5/056102
Full Text: [PDF 547 KB] (Downloads:744)
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The interaction between a wedge disclination dipole and a crack emanating from a semi-elliptic hole is investigated. Utilising the complex variable method, the closed form solutions are derived for complex potentials and stress fields. The stress intensity factor at the tip of the crack and the image force acting on the disclination dipole center are also calculated. The influence of the morphology of the blunt crack and the position of the disclination dipole on the shielding effect to the crack and the image force is examined in detail. The results indicate that the shielding or anti-shielding effect to the stress intensity factor increases when the wedge disclination dipole approaches the tip of the crack. The effects of the morphology of the blunt crack on the stress intensity factor of the crack and the image force are very significant.

Radiation effects on MOS and bipolar devices by 8 MeV protons, 60 MeV Br ions and 1 MeV electrons

Li Xing-Ji, GengHong-Bin, Lan Mu-Jie, Yang De-Zhuang, He Shi-Yu, Liu Chao-Ming
Chin. Phys. B, 2010, 19 (5): 056103 doi: 10.1088/1674-1056/19/5/056103
Full Text: [PDF 2089 KB] (Downloads:960)
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The radiation effects of the metal-oxide-semiconductor (MOS) and the bipolar devices are characterised using 8~MeV protons, 60~MeV Br ions and 1~MeV electrons. Key parameters are measured {\it in-situ} and compared for the devices. The ionising and nonionising energy losses of incident particles are calculated using the Geant4 and the stopping and range of ions in matter code. The results of the experiment and energy loss calculation for different particles show that different incident particles may give different contribution to MOS and bipolar devices. The irradiation particles, which cause larger displacement dose within the same chip depth of bipolar devices at a given total dose, would generate more severe damage to the voltage parameters of the bipolar devices. On the contrary, the irradiation particles, which cause larger ionising damage in the gate oxide, would generate more severe damage to MOS devices. In this investigation, we attempt to analyse the sensitivity to radiation damage of the different parameter of the MOS and bipolar devices by comparing the irradiation experimental data and the calculated results using Geant4 and SRIM code.

First-principles study of electronic and optical properties in wurtzite Zn1-xCuxO

Zhao Long, Lu Peng-Fei, Yu Zhong-Yuan, Liu Yu-Min, Wang Dong-Lin, Ye Han
Chin. Phys. B, 2010, 19 (5): 056104 doi: 10.1088/1674-1056/19/5/056104
Full Text: [PDF 1404 KB] (Downloads:1763)
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We perform a first-principles simulation to study the electronic and optical properties of wurtzite Zn$_{1 - x}$Cu$_{x}$O. The simulations are based upon the Perdew--Burke--Ernzerhof form of generalised gradient approximation within the density functional theory. Calculations are carried out in different concentrations. With increasing Cu concentration, the band gap of Zn$_{1 - x}$Cu$_{x}$O decreases due to the shift of valence band. The imaginary part of the dielectric function indicates that the optical transition between O 2p states in the highest valence band and Zn 4s states in the lowest conduction band shifts to the low energy range as the Cu concentration increases. Besides, it is shown that the insertion of Cu atom leads to redshift of the optical absorption edge. Meanwhile, the optical constants of pure ZnO and Zn$_{0.75}$Cu$_{0.25}$O, such as loss function, refractive index and reflectivity, are discussed.

Stabilisation analysis of multiple car-following model in traffic flow

Peng Guang-Han
Chin. Phys. B, 2010, 19 (5): 056401 doi: 10.1088/1674-1056/19/5/056401
Full Text: [PDF 1054 KB] (Downloads:990)
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An improved multiple car-following model is proposed by considering the arbitrary number of preceding cars, which includes both the headway and the velocity difference of multiple preceding cars. The stability condition of the extended model is obtained by using the linear stability theory. The modified Korteweg--de Vries equation is derived to describe the traffic behaviour near the critical point by applying the nonlinear analysis. Traffic flow can be also divided into three regions: stable, metastable and unstable regions. Numerical simulation is accordance with the analytical result for the model. And numerical simulation shows that the stabilisation of traffic is increasing by considering the information of more leading cars and there is unavoidable effect on traffic flow from the multiple leading cars' information.

Shock-induced phase transition and spalling characteristic in pure iron and FeMnNi alloy

Chen Yong-Tao, Tang Xiao-Jun, Li Qing-Zhong
Chin. Phys. B, 2010, 19 (5): 056402 doi: 10.1088/1674-1056/19/5/056402
Full Text: [PDF 1511 KB] (Downloads:1043)
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This paper provides an investigation of the phase transition and spalling characteristic induced during shock loading and unloading in the pure iron and the FeMnNi alloy. The impact for the pure iron is symmetric and with same-thickness for both the flyer and the target plate. It is found that an abnormal multiple spalling happens in the pure iron sample as the pressure exceeds the $\alpha -\varepsilon $ transition threshold of 13 GPa. In the symmetric and same-thickness impact and reverse impact experiments of the FeMnNi alloy, two abnormal tension regions occur when the pressure exceeds the $\alpha -\varepsilon $ transition threshold of 6.3~GPa, and the reverse phase transition $\varepsilon -\alpha $ begins below 4.2~GP. The experimental process is simulated successfully from the non-equilibrium mixture phase and Boettger's model. Such abnormal spalling phenomena are believed to relate to the shocked $\alpha -\varepsilon $ phase transition. The possible reasons for the abnormal multiple spalling, which occurs during the symmetric and same-thickness impact experiments of pure iron and FeMnNi alloy, are discussed.

Solving the initial condition of the string relaxation equation of the string model for glass transition: part-I

Zhang Jin-Lu, Wang Li-Na, Zhou Heng-Wei, Zhang Li-Li, Zhao Xing-Yu, Huang Yi-Neng
Chin. Phys. B, 2010, 19 (5): 056403 doi: 10.1088/1674-1056/19/5/056403
Full Text: [PDF 175 KB] (Downloads:717)
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The string model for the glass transition can quantitatively describe the universal $\alpha $-relaxation in glassformers, including the average relaxation time, the distribution function of the relaxation time, and the relaxation strength as functions of temperature. The string relaxation equation (SRE) of the model, at high enough temperatures, simplifies to the well-known single particle mean-field Debye relaxation equation, and at low enough temperatures to the well-known Rouse--Zimm relaxation equation that describes the relaxation dynamics of linear macromolecules. However, its initial condition, necessary to the further model predictions of glassy dynamics, has not been solved. In this paper, the special initial condition (SIC) of the SRE, i.e. for straight strings and the dielectric spectrum technique that is one of the most common methods to measure the glassy dynamics, was solved exactly. It should be expected that the obtained SIC would benefit the solution of the general initial condition of the SRE of the string model, i.e. for stochastically spatially configurating strings, as will be described in separate publications.

A molecular dynamics simulation of segregation behaviours of horizontally vibrated binary granular mixture

Xia Ji-Hong, You Yu-Wei, WangPan-Pan, Wang Wei-Lu, Liu Chang-Song
Chin. Phys. B, 2010, 19 (5): 056404 doi: 10.1088/1674-1056/19/5/056404
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This paper performs the two-dimensional, soft-sphere molecular dynamics simulations to study the granular segregation in a binary granular mixture with the same size but different density in the container with the sawtooth base under horizontal vibration. The segregation phase diagram is presented in the acceleration-frequency space. When the acceleration is high enough to result in relative motions of the particles, the system can be in various states (mixed state, vertical and horizontal segregation state), which depend on both acceleration and frequency. Due to the sawtooth base there is stratified flow effect besides density effect. The density effect raises the light particles. The stratified flow drives the particles in the upper levels to the right and the particles in the lower particles to the left, those fact results in the appearance of the left segregation state. The left segregation state can be changed to the right segregation by changing the shape of the sawtooth. As the vibration frequency increases, the stratified flow effect becomes weaker and weaker, so at high vibration frequencies the vertical segregation state appears instead of the left segregation state.

Superhydrophobic surfaces via controlling the morphology of ZnO micro/nano complex structure

Gong Mao-Gang, Xu Xiao-Liang, Yang Zhou, Liu Yan-Song, Liu Ling
Chin. Phys. B, 2010, 19 (5): 056701 doi: 10.1088/1674-1056/19/5/056701
Full Text: [PDF 2459 KB] (Downloads:1315)
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ZnO micro/nano complex structure films, including reticulate papillary nodes, petal-like and flake-hole, have been self-assembled by a hydrothermal technique at different temperatures without metal catalysts. The wettability of the above film surfaces was modified with a simple coating of heptadecafluorodecyltrimethoxy-silane in toluene. After modifying, the surface of ZnO film grown at 50~${^\circ}$C was converted from superhydrophilic with a water contact angle lower than 5$^{\circ}$ to superhydrophobic with a water contact angle of 165$^{\circ}$. Additionally, the surface of reticulate papillary nodes ZnO film grown at 100~${^\circ}$C had excellent superhydrophobicity, with a water contact angle of 173$^{\circ}$ and a sliding angle lower than 2$^{\circ}$. Furthermore, the water contact angle on the surface of petal-like and flake-hole ZnO films grown at 150~${^\circ}$C and 200~${^\circ}$C were found to be 140$^{\circ}$ and 120$^{\circ}$, respectively. The wettability for the samples was found to depend strongly on the surface morphology which results from the growth temperature.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

First-principles calculation of magnetism of icosahedral Fe clusters

Cheng Zhi-Da, Ling Tao, Zhu Jing
Chin. Phys. B, 2010, 19 (5): 057101 doi: 10.1088/1674-1056/19/5/057101
Full Text: [PDF 2018 KB] (Downloads:604)
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Icosahedral iron clusters are synthesized and characterized in our group by using experimental methods. But the measurements of magnetic properties still face difficulties: the sizes of the clusters and the amount of product. Therefore theoretical methods are employed to study these issues. In this paper, icosahedral iron clusters containing 13, 55, 147, 309 atoms are calculated by {\em ab initio} techniques. After the structural relaxation, the magnetism of the clusters is found to be similar to that of face centred cubic (FCC) iron with stronger ferromagnetism on surface. But the central atom of each cluster is exceptional, which has a smaller magnetic moment. We also study the electronic structural properties in the clusters for the better explanation of the magnetism. It is suggested that in small clusters, the magnetic properties still depend on the local structural arrangement.

Molecular dynamics simulation of collective behaviour of Xe in UO2

Tian Xiao-Feng, Long Chong-Sheng, Zhu Zheng-He, Gao Tao
Chin. Phys. B, 2010, 19 (5): 057102 doi: 10.1088/1674-1056/19/5/057102
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This paper performs atomic simulations of the nucleation and growth of Xe bubble in UO$_{2}$ at 1600~K. The bubble growth was simulated up to the bubble containing 50 Xe atoms. The Xe atoms were added directly to the bubble one by one, followed by a relaxation of the system for several picoseconds. The simulations estimated the bubble pressure and radius at different Xe concentrations. The results indicate that the bubble pressure drops with the increasing Xe/U and bubble size at low Xe concentration, while the pressure will increase with the Xe/U ratio at high Xe concentration. The swelling of the system associated with the bubble growth was also obtained. Finally, the recovery of the damaged structure was investigated.

Field emission of carbon nanotube array with normal-gate cold cathode

Dai Jian-Feng, Mu Xiao-Wen, Qiao Xian-Wu, Chen Xiao-Ting, Wang Jun-Hong
Chin. Phys. B, 2010, 19 (5): 057201 doi: 10.1088/1674-1056/19/5/057201
Full Text: [PDF 923 KB] (Downloads:684)
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A hexagon pitch carbon nanotube (CNT) array vertical to the normal gate of cold cathode field emission displayer (FED) is simulated by solving the Laplace equation. The calculated results show that the normal gate causes the electric field around the CNT tops to be concentrated and emission electron beam become a column. The field enhancement factor and the emission current intensity step up greatly compared with those of diode structure. Emission current density increases rapidly with the decrease of normal-gate aperture. The gate voltage exerts a critical influence on the emission current.

Influence of time-periodic potentials on electronic transport in double-well structure

Li Chun-Lei, Xu Yan
Chin. Phys. B, 2010, 19 (5): 057202 doi: 10.1088/1674-1056/19/5/057202
Full Text: [PDF 475 KB] (Downloads:510)
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Within the framework of the Floquet theorem, we have investigated single-electron photon-assisted tunneling in a double-well system using the transfer matrix technique. The transmission probability displays satellite peaks on the both sides of main resonance peaks and these satellite peaks originate from emission or absorption photons. The single-electron resonance tunneling can be control through changing applied harmonically potential positions, such as driven potential in wells, in barriers, or in whole double-well system. This advantage should be useful in the optimization of the parameters of a transmission device.

Comparative study of different properties of GaN films grown on(0001) sapphire using high and low temperature AlN interlayers

Xue Jun-Shuai, Hao Yue, Zhang Jin-Cheng, Ni Jin-Yu
Chin. Phys. B, 2010, 19 (5): 057203 doi: 10.1088/1674-1056/19/5/057203
Full Text: [PDF 187 KB] (Downloads:784)
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Comparative study of high and low temperature AlN interlayers and their roles in the properties of GaN epilayers prepared by means of metal organic chemical vapour deposition on (0001) plane sapphire substrates is carried out by high resolution x-ray diffraction, photoluminescence and Raman spectroscopy. It is found that the crystalline quality of GaN epilayers is improved significantly by using the high temperature AlN interlayers, which prevent the threading dislocations from extending, especially for the edge type dislocation. The analysis results based on photoluminescence and Raman measurements demonstrate that there exist more compressive stress in GaN epilayers with high temperature AlN interlayers. The band edge emission energy increases from 3.423~eV to 3.438~eV and the frequency of Raman shift of $E_{2 }$(TO) moves from 571.3~cm$^{ - 1}$ to 572.9~cm$^{ - 1}$ when the temperature of AlN interlayers increases from 700~$^{\circ}$C to 1050~$^{\circ}$C. It is believed that the temperature of AlN interlayers effectively determines the size, the density and the coalescence rate of the islands, and the high temperature AlN interlayers provide large size and low density islands for GaN epilayer growth and the threading dislocations are bent and interactive easily. Due to the threading dislocation reduction in GaN epilayers with high temperature AlN interlayers, the approaches of strain relaxation reduce drastically, and thus the compressive stress in GaN epilayers with high temperature AlN interlayers is high compared with that in GaN epilayers with low temperature AlN interlayers.

Fabrication of a 256-bits organic memory by soft x-ray lithography

Liu Xing-Hua, Lu Wen-Sheng, Ji Zhuo-Yu, Tu De-Yu, Zhu Xiao-Li, Xie Chang-Qing, Liu Ming
Chin. Phys. B, 2010, 19 (5): 057204 doi: 10.1088/1674-1056/19/5/057204
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This paper reports a procedure of soft x-ray lithography for the fabrication of organic crossbar structure. Electron beam lithography is employed to fabricate the mask for soft x-ray lithography, with direct writing technology to lithograph positive resist, polymethyl methacrylate on the polyimide film. Then Au is electroplated on the polyimide film. Hard contact mode exposure is used in x-ray lithography to transfer the graph from the mask to the wafer. The 256-bits organic memory is achieved with the critical dimension of 250~nm.

The effect of initial discharge conditions on the properties of microcrystalline silicon thin films and solar cells

Chen Yong-Sheng, Yang Shi-E, Wang Jian-Hua, Lu Jing-Xiao, Gao Xiao-Yong, Gu Jin-Hua
Chin. Phys. B, 2010, 19 (5): 057205 doi: 10.1088/1674-1056/19/5/057205
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This paper studies the effects of silane back diffusion in the initial plasma ignition stage on the properties of microcrystalline silicon ($\mu $c-Si:H) films by Raman spectroscopy and spectroscopic ellipsometry, through delaying the injection of SiH$_{4}$ gas to the reactor before plasma ignition. By comparing with standard discharge condition, delayed SiH$_{4}$ gas condition could prevent the back diffusion of SiH$_{4}$ from the reactor to the deposition region effectively, which induced the formation of a thick amorphous incubation layer in the interface between bulk film and glass substrate. Applying this method, it obtains the improvement of spectral response in the middle and long wavelength region by combining this method with solar cell fabrication. Finally, results are explained by modifying zero-order analytical model, and a good agreement is found between model and experiments concerning the optimum delayed injection time.

Size effect of quantum conductance in carbon nanotube Y-Junctions

Liu Hong
Chin. Phys. B, 2010, 19 (5): 057206 doi: 10.1088/1674-1056/19/5/057206
Full Text: [PDF 1591 KB] (Downloads:499)
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This paper studies the quantum conductance properties of three-terminated carbon nanotube Y-junctions, which are built by connecting three (5,5) single-walled carbon nanotubes. The results show that the quantum conductance at the Fermi energy oscillates periodically with the junction's size, and the number of oscillating periodic layers is 3 which is the same as that in the two terminated $(10,0)/m(5,5)/(10,0)$ junctions. Moreover, this Y-junction with different size exhibits obvious different distribution of electron current in the two drain branches, called shunt valve effect of electronic current. Thus the degree of this effect can be controlled and modulated directly by constructing the three branches' sizes or the distribution of defect. The results show in detail that the difference between the two drain currents can be up to two times for some constructions with special sizes. In addition, the uniform distribution of defects in the Y-junction leads to lower quantum conductance than that of other defect configurations.

The initial decoherence of the mesoscopic Josephson junction flux qubit

Su Jie, Wang Ji-Suo, Zhang Xiao-Yan, Liang Bao-Long
Chin. Phys. B, 2010, 19 (5): 057301 doi: 10.1088/1674-1056/19/5/057301
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For a mesoscopic radio frequency superconducting quantum interference device (rfSQUID), at a degeneracy point, the system reduces to a quantum two-state system which can be used as a flux qubit. When the noise environment is equivalent to a harmonic oscillators bath, by virtue of an operator-norm measure for the short time decoherence, this paper investigates the initial decoherence of the flux qubit operating in the ohmic noise environment and illustrates its property by means of the numerical evaluation.

Comparative studies of Ge and Si p-channel metal-oxide-semiconductor field-effect-transistors with HfSiON dielectric and TaN metal gate

Hu Ai-Bin, Xu Qiu-Xia
Chin. Phys. B, 2010, 19 (5): 057302 doi: 10.1088/1674-1056/19/5/057302
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Ge and Si p-channel metal--oxide--semiconductor field-effect-transistors (p-MOSFETs) with hafnium silicon oxynitride (HfSiON) gate dielectric and tantalum nitride (TaN) metal gate are fabricated. Self-isolated ring-type transistor structures with two masks are employed. W/TaN metal stacks are used as gate electrode and shadow masks of source/drain implantation separately. Capacitance--voltage curve hysteresis of Ge metal--oxide--semiconductor (MOS) capacitors may be caused by charge trapping centres in GeO$_{x}$ ($1

Characteristics and parameter extraction for NiGe/n-type Ge Schottky diode with variable annealing temperatures

Liu Hong-Xia, Wu Xiao-Feng, Hu Shi-Gang, Shi Li-Chun
Chin. Phys. B, 2010, 19 (5): 057303 doi: 10.1088/1674-1056/19/5/057303
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Current transport mechanism in Ni-germanide/n-type Ge Schottky diodes is investigated using current--voltage characterisation technique with annealing temperatures from 300~\duto 500~\du. Based on the current transport model, a simple method to extract parameters of the NiGe/Ge diode is presented by using the $I$--$V$ characteristics. Parameters of NiGe/n-type Ge Schottky diodes fabricated for testing in this paper are as follows: the ideality factor $n$, the series resistance $R_{\rm s}$, the zero-field barrier height $\phi _{\rm b0}$, the interface state density $D_{\rm it}$, and the interfacial layer capacitance $C_{\rm i}$. It is found that the ideality factor $n$ of the diode increases with the increase of annealing temperature. As the temperature increases, the interface defects from the sputtering damage and the penetration of metallic states into the Ge energy gap are passivated, thus improving the junction quality. However, the undesirable crystallisations of Ni-germanide are observed together with NiGe at a temperature higher than 400~\du. Depositing a very thin ($\sim $1~nm) heavily Ge-doped $n^{+}$ Ge intermediate layer can improve the NiGe film morphology significantly.

Effect of interface roughness on the carrier transport in germanium MOSFETs investigated by Monte Carlo method

Du Gang, Liu Xiao-Yan, Xia Zhi-Liang, Yang Jing-Feng, Han Ru-Qi
Chin. Phys. B, 2010, 19 (5): 057304 doi: 10.1088/1674-1056/19/5/057304
Full Text: [PDF 289 KB] (Downloads:533)
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Interface roughness strongly influences the performance of germanium metal--organic--semiconductor field effect transistors (MOSFETs). In this paper, a 2D full-band Monte Carlo simulator is used to study the impact of interface roughness scattering on electron and hole transport properties in long- and short- channel Ge MOSFETs inversion layers. The carrier effective mobility in the channel of Ge MOSFETs and the in non-equilibrium transport properties are investigated. Results show that both electron and hole mobility are strongly influenced by interface roughness scattering. The output curves for 50~nm channel-length double gate n and p Ge MOSFET show that the drive currents of n- and p-Ge MOSFETs have significant improvement compared with that of Si n- and p-MOSFETs with smooth interface between channel and gate dielectric. The $82\%$ and $96\%$ drive current enhancement are obtained for the n- and p-MOSFETs with the completely smooth interface. However, the enhancement decreases sharply with the increase of interface roughness. With the very rough interface, the drive currents of Ge MOSFETs are even less than that of Si MOSFETs. Moreover, the significant velocity overshoot also has been found in Ge MOSFETs.

Giant magnetocaloric effect in Tb5Ge2-xSi2-xMn2x compounds Hot!

E. Yüzüak, B. Emre, Y. Elerman, A. Yücel
Chin. Phys. B, 2010, 19 (5): 057501 doi: 10.1088/1674-1056/19/5/057501
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The crystal structure, magnetic and magnetocaloric characteristics of the pseduo ternary compounds of Tb$_{5}$Ge$_{2-x}$Si$_{2-x}$Mn$_{2x}$ (0 $\leq $ 2$x$ $\leq$ 0.1) were investigated by x-ray powder diffraction and magnetization measurements. The x-ray powder diffraction results show that all compounds preserve the monoclinic phase as the majority phase and all the synthesized compounds were observed to be ferromagnetic from magnetization measurements. Magnetic phase transitions were interpreted in terms of Landau theory. Maximum isothermal magnetic entropy change value (20.84~J\,$\cdot$\,kg$^{-1}$\,$\cdot$\,K$^{-1}$) was found for Tb$_{5}$Ge$_{1.95}$Si$_{1.95}$Mn$_{0.1}$ at around 123~K in the magnetic field change of 5~T.

First-order reversal curves of magnetic recording tapes

Yin Jin-Hua, Pan Li-Qing
Chin. Phys. B, 2010, 19 (5): 057502 doi: 10.1088/1674-1056/19/5/057502
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The interaction and its variation between magnetic grains in two kinds of magnetic recording tapes are investigated by first-order reversal curves (FORC) and the $\delta M$ method. The composition and microstructure of the samples are characterised by x-ray diffraction and scanning electron microscope. The FORC diagram can provide more accurate information of the interaction and its variation, but the $\delta M$ curves cannot. The positive interaction field and the large variation of the interaction field have opposite effects on the $\delta M$ curve.

Effect of F doping on capacitance-voltage characteristics of SiCOH low-k films metal-insulator-semiconductor structure

Ye Chao, Ning Zhao-Yuan
Chin. Phys. B, 2010, 19 (5): 057701 doi: 10.1088/1674-1056/19/5/057701
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This paper investigates the capacitance--voltage ($C$--$V$) characteristics of F doping SiCOH low dielectric constant films metal--insulator--semiconductor structure. The F doping SiCOH films are deposited by decamethylcyclopentasiloxane (DMCPS) and trifluromethane (CHF$_{3})$ electron cyclotron resonance plasmas. With the CHF$_{3}$/DMCPS flow rate ratio from 0 to 0.52, the positive excursion of $C$--$V$ curves and the increase of flat-band voltage $V_{\rm FB}$ from $-6.1$~V to 32.2~V are obtained. The excursion of $C$--$V$ curves and the shift of $V_{\rm FB}$ are related to the change of defects density and type at the Si/SiCOH interface due to the decrease of Si and O concentrations, and the increase of F concentration. At the CHF$_{3}$/DMCPS flow rate ratio is 0.12, the compensation of F-bonding dangling bond to Si dangling bond leads to a small $V_{\rm FB}$ of 2.0~V.

Negative refraction in ferromagnetic materials under external magnetic field: a theoretical analysis

Wei Jing-Song, Xiao Mu-Fei
Chin. Phys. B, 2010, 19 (5): 057801 doi: 10.1088/1674-1056/19/5/057801
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We present a detailed theoretical analysis on the possibilities and conditions for negative permeability and negative refraction occuring in the magnetic materials with both pronounced magnetic and dielectric responses to electromagnetic waves. The results indicate that the permeability is always positive for $\de=(2q+0.5)\pi$ ($\de$ is the initial phase difference of magnetic components $h_{x}$ and $h_{y }$ of incident electromagnetic wave, $q$ is integer), which means that it is difficult to realize negative refraction. However, for $\de=2q\pi, \de=(2q+1)\pi$, or $\de=(2q-0.5)\pi$, the negative permeability occurs at some range of free procession frequency, which means that the refraction can become negative under certain conditions. Further analysis reveals that for general positive permittivity there are various opportunities for realizing the negative refraction provided that some requirements are met. One concludes also that the refractive index for $\de=2q\pi$ case is similar to $\de=(2q+1)\pi$. The only difference between two cases of $\de=2q\pi$ and $\de=(2q+1)\pi$ is that the $x$-direction for $\de=2q\pi$ corresponds to the $y$-direction for $\de=(2q+1)\pi$, and the $y$-direction for $\de=2q\pi$ corresponds to the $x$-direction for $\de=(2q+1)\pi$. The results are valuable for designing and analysing the complex negative refraction of magnetic materials.

Role of Ga vacancies in enhancing the leakage current of GaN Schottky barrier ultraviolet photodetectors

Zhao De-Gang, Zhang Shuang, Liu Wen-Bao, Jiang De-Sheng, Zhu Jian-Jun, Liu Zong-Shun, Wang Hui, Zhang Shu-Ming, Yang Hui, Hao Xiao-Peng, Wei Long
Chin. Phys. B, 2010, 19 (5): 057802 doi: 10.1088/1674-1056/19/5/057802
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The leakage current of GaN Schottky barrier ultraviolet photodetectors is investigated. It is found that the photodetectors adopting undoped GaN instead of lightly Si-doped GaN as an active layer show a much lower leakage current even when they have a higher dislocation density. It is also found that the density of Ga vacancies in undoped GaN is much lower than in Si-doped GaN. The Ga vacancies may enhance tunneling and reduce effective Schottky barrier height, leading to an increase of leakage current. It suggests that when undoped GaN is used as the active layer, it is necessary to reduce the leakage current of GaN Schottky barrier ultraviolet photodetector.

A novel yellow emitting phosphor Dy3+, Bi3+ co-doped YVO4 potentially for white light emitting diodes

Ci Zhi-Peng, Wang Yu-Hua, Zhang Jia-Chi
Chin. Phys. B, 2010, 19 (5): 057803 doi: 10.1088/1674-1056/19/5/057803
Full Text: [PDF 194 KB] (Downloads:1137)
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Novel Y$_{1 - x - y}$VO$_{4}$:$x$Dy$^{3 + }$, $y$Bi$^{3 + }$ ($0.01 \le x \le 0.05, 0 \le y \le 0.20$) phosphors for light emitting diode (LED) were successfully synthesised by solid-state reaction. The calculation results of electronic structure show that YVO$_{4}$ has a direct band gap with 3~eV at $G$. The top of the valence band is dominated by O 2p state and the bottom of the conduction band is mainly composed of O 2p and V 3d states. An efficient yellow emission under near-ultraviolet (365 nm) excitation is observed. Compared with the pure YVO$_{4}$:Dy$^{3 + }$ samples, the Dy$^{3 + }$, Bi$^{3 + }$ co-doped samples show a more intensive emission peak (at 574~nm) and a new broad emission band (450--770~nm), due to the $^{4}F_{9 / 2}-{}^{6}H_{13 / 2 }$ transition of Dy$^{3 + }$ and the emission of the VO$_{4}^{3 - }-$Bi$^{3 + }$ complex respectively. The optimum chromaticity index of Y$_{1 - x - y}$VO$_{4}$:$x$Dy$^{3 + }$, $y$Bi$^{3 + }$ ($0.01 \le x \le 0.05, 0 \le y \le 0.20$) is (0.447, 0.497), which indicates that YVO$_{4}$:Dy$^{3 + }$, Bi$^{3 + }$ has higher colour saturation than the commercial phosphor YAG: Ce$^{3 + }$. The effects of concentration of Dy$^{3 + }$, Bi$^{3 + }$, electric states and the photoluminescence properties are discussed in details.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

A two scale nonlinear fractal sea surface model in a one dimensional deep sea

Xie Tao, Zou Guang-Hui, WilliamPerrie, Kuang Hai-Lan, Chen Wei
Chin. Phys. B, 2010, 19 (5): 059201 doi: 10.1088/1674-1056/19/5/059201
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Using the theory of nonlinear interactions between long and short waves, a nonlinear fractal sea surface model is presented for a one dimensional deep sea. Numerical simulation results show that spectra intensity changes at different locations (in both the wave number domain and temporal-frequency domain), and the system obeys the energy conservation principle. Finally, a method to limit the fractal parameters is also presented to ensure that the model system does not become ill-posed.
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